In multicarrier communications, reporting of downlink (DL) information on the uplink (UL) is typically performed for one DL carrier at a time. Therefore, existing multicarrier communication systems are lacking techniques for reporting control information on the UL for more than one concurrent DL carriers.
For example, a Third Generation Partnership Project (3GPP) long term evolution (LTE) system is a multicarrier communications system. For the LTE DL direction, a transmission scheme based on an orthogonal frequency division multiple access (OFDMA) air interface is used. According to OFDMA, a wireless transmit/receive unit (WTRU) may be allocated by an evolved Node-B (eNB) to receive its data anywhere across the entire LTE transmission bandwidth. For the LTE UL direction, single-carrier (SC) transmission is used based on discrete Fourier transform-spread-OFDMA (DFT-S-OFDMA), or equivalently, single carrier frequency division multiple access (SC-FDMA). A WTRU will transmit in the LTE UL direction only on a limited, yet contiguous set of assigned sub-carriers in an FDMA arrangement.
FIG. 1 illustrates the mapping of a transport block 10 to an LTE carrier 20, for UL or DL transmission. Layer 1 (L1) 30 receives information from a hybrid automatic repeat request (HARQ) entity 40 and a scheduler 50, and uses it to assign a transport block 10 to the LTE carrier 20. As shown in FIG. 1, a UL or DL LTE carrier 20, or simply a carrier 20, is made up of multiple sub-carriers 60. An eNB may receive a composite UL signal across the entire transmission bandwidth from one or more WTRUs at the same time, where each WTRU transmits on a subset of the available transmission bandwidth or sub-carriers.
LTE-Advanced (LTE-A) is currently being developed by the 3GPP standardization body in order to further improve achievable throughput and coverage of LTE-based radio access systems, and to meet the international mobile telecommunications (IMT) advanced requirements of 1 Gbps and 500 Mbps in the DL and UL directions, respectively. Among the improvements proposed for LTE-A are carrier aggregation and support of flexible bandwidth arrangements. LTE-A proposes to allow DL and UL transmission bandwidths to exceed the 20 MHz limit in LTE, for example, permitting 40 MHz or 100 MHz bandwidths. In this case, a carrier may occupy the entire frequency block. LTE-A proposes to allow for more flexible usage of the available paired spectrum. For example, LTE may be limited to operate in symmetrical and paired FDD mode where, for example, both the DL and UL may have 10 MHz (or 20 MHz) transmission bandwidths.
In contrast, LTE-A proposes to also operate in asymmetric configurations where, for example, a DL bandwidth of 10 MHz may be paired with a UL bandwidth of 5 MHz. In addition, LTE-A proposes composite aggregate transmission bandwidths, that may be backwards compatible with LTE. By way of example, the DL may include a first 20 MHz carrier plus a second 10 MHz carrier, which is paired with a UL 20 MHz carrier. Carriers transmitted concurrently in the same UL or DL direction are referred to as component carriers (CCs). The composite aggregate transmission bandwidths of the CCs may not necessarily be contiguous in the frequency domain. Continuing the example, the first 10 MHz CC may be spaced by 22.5 MHz in the DL band from the second 5 MHz DL CC. Alternatively, operation may use contiguous aggregate transmission bandwidths. By way of example, a first DL CC of 15 MHz may be aggregated with another 15 MHz DL CC and paired with a UL carrier of 20 MHz.
In the LTE system DL direction, WTRUs receive their data (and in some cases their control information) on the physical downlink shared channel (PDSCH). The transmission of the PDSCH is scheduled and controlled by the eNB using a DL scheduling assignment, which is carried on a physical downlink control channel (PDCCH). As part of the DL scheduling assignment, the WTRU receives control information on the modulation and coding scheme (MCS) and DL resources allocation, (i.e., the indices of allocated resource blocks). Then, if a scheduling assignment is received, the WTRU decodes its allocated PDSCH resources on the correspondingly allocated DL resources.
In the LTE-A radio access system, at least one PDSCH may be transmitted to a WTRU on more than one assigned CC. Using the carrier aggregation mechanism, different approaches for allocating PDSCH resources on more than one CC have been proposed.
In an LTE-A system, the PDCCHs, (or downlink control information (DCI) messages contained therein carrying the assignment information), may be separately transmitted for the CCs containing the accompanying PDSCH transmissions. For example, if there are two CCs, there are two separate DCI messages on each CC corresponding to the PDSCH transmissions on each CC, respectively. Alternatively, the two separate DCI messages for the WTRU may be sent on one CC, even though they may pertain to accompanying data, or PDSCH transmissions on different CCs. The separate DCI messages of PDCCHs for at least one WTRU may be transmitted in one or in multiple carriers, and not necessarily all of them on every CC. For example, a first DCI transmission on the PDCCH pertaining to the PDSCH allocation on a first CC is also contained on this first CC, but the second DCI to that WTRU PDCCH transmission pertaining to the PDSCH allocation on a second CC is contained on this second CC.
The DCI carrying the assignment information for PDSCHs on more than one CC may be encoded jointly and carried by one single joint DCI control message, or PDCCH message. For example, a single DCI or PDCCH or control message carrying an assignment of PDSCHs or data resources on two CCs is received by the WTRU. Alternatively, the joint PDCCH for a WTRU or group of WTRUs may be transmitted in one or multiple carriers.
In an LTE-A system using carrier aggregation, one asymmetrical scenario occurs whereby a WTRU is configured with a higher number of DL carriers than UL carriers. A one one-to-one mapping between a given DL carrier and a UL carrier cannot be performed as it is the case for LTE.
Of particular interest is the UL carrier assignment for the physical uplink control channel (PUCCH), which is used to carry the HARQ feedback, and the channel quality indicator (CQI)/precoding matrix indicator (PMI)/rank indicator (RI). Furthermore, there is interest in UL carrier assignment of the scheduling request (SR) on a physical random access channel (PRACH), and the buffer status and power headroom reporting on the UL synchronization channel. If more than one DL carrier is mapped to a single UL carrier, (i.e., a single PUCCH), collisions may potentially be created in the L1 HARQ feedback.